Environment Southland’s latest monitoring has found high levels of potentially toxic algae in the Mataura River at the Mataura Island Bridge.
A spokeswoman said water users should be vigilant and avoid contact with water and the algae, and swimming in the Mataura River near Mataura township should be avoided.
Similar growth could be occurring in other rivers and tributaries, so waterway users were advised to be vigilant across Murihiku-Southland.
The spokeswoman said algae occurred naturally in waterways and could flourish during fine conditions and periods of stable river flows. Most algae were harmless; however, some cyanobacteria could produce toxins and rapidly bloom to high levels.
"These algae are potentially toxic and can be commonly identified in waterways as a dark green/brown slime on rocks, or dark brown/black mats at the water’s edge. The toxins these algae can produce are harmful to people and animals if swallowed, or through contact with skin."
She said people should keep dogs on a lead and children away from affected waterways.
"If you experience health symptoms after contact with contaminated water, visit a doctor immediately. If you are concerned any animals have consumed toxic algae or contaminated water, they should be taken to a vet immediately."
